German Patent No. 3,420,528 A1 discloses a height-adjustable column in which a height-changing mechanism, in this case a pneumatic spring, is received within a stationary tube. Such a height-adjustable column is widely employed in the furniture industry, especially in connection with chairs, and has been quite successful.
German Patent No. 4,034,633 A1 and German Patent No. 4,212,282 A1 disclose enhancements of height-adjustable columns in which a telescoping guide tube is provided between the stationary tube and the height-changing mechanism for the purpose of increasing the guide length of the pneumatic spring. The guide tube is pushed out to an extent that depends on the height setting of the column and the pneumatic spring.